HYPERTENSIVE SUBPOPULATIONS AS DEFINED BY THEIR NATRIURETIC RESPONSE TO AMBULATION

BACKGROUND: The heterogeneity among patients with essential hypertensi on is Known. We observed in an earlier study a large spread in the val ues of fractional excretion of sodium in a group of subjects with mild essential hypertension after ambulation, suggesting possible subgroup s among them. We defined as the reteiner(R) group that wich presented a reabsorption index (RI = fractional excretion of sodium during supin e/fractional excretion of sodium after ambulation) < 2.5 and the non-r eteiner(NR) group as that whose RI < 2.5. We analyzed at what level th e reabsorption of Na was produced and the differences between the poss ible groups. PATIENTS AND METHODS: We studied 51 mild essential hypert ensive patients, 22 men and 29 women, in two consecutive periods -recu mbent, 90 minutes; ambulation, 90 minutes-. We calculated the clearanc e of creatinine and lithium, fractional proximal and distal reabsorpti on of Na, plasma renin activity (PRA), plasma aldosterone (ALDO) and e limination of PGE, and kallikrein in the urine; the plasma catecholami nes at the end of the recumbent position and after 10 minutes in the u pright position. The study was taken after at least ten days without t reatment and following a diet with free Na intake. RESULTS: We did not encounter significant differences between the reteiner (n = 19) and n on-reteiner (32) group with regard to age, sex, body mass index or eli mination of Na/24 h. The lower natriuresis in ambulation in the R grou p compared with the NR group is due to a higher fractional reabsorptio n of sodium, proximal (83.7 +/- 4.9% vs 79 +/- 5.2; p < 0.01) as well as distal (96.8 +/- 2 vs 95.3 +/- 2%; p < 0.05. The increment in the P RA was greater in the R group (1.3 +/- 1.4 vs 0.8 +/- 0.8; p < 0.05) a fter ambulation; in the R group showed a tower index -increment in ALD O/increment in PRA- in response to postural change although without si gnificancy. We observed a lower elimination of PGE(2) and kallikrein i n the R group as compaired with NR group (p < 0.05), We did not find d ifferences with regard to plasma catecholamines. CONCLUSIONS: Ambulati on allows to distinguish two groups of essential hypertensive patients according to natriuresis. The lower natriuresis in ambulation on the part of the R group could be due to the increase in PRA and therefore of the angiotensin Ii at the level of the proximal tubule, and to a lo wer activity of natriuretic hormones (PGE(2) kallikrein) at the distal level.